Detonation suppression piston for internal-combustion engines



Dec. 15, 1953 A. G. BODINE, JR DEITONATION SUPPRESSION PISTON FORINTERNAL-COMBUSTION ENGINES Filed Feb. 25, 1952 INVENTOR. 41 B527 6.Baa/Mafia Patented Dec. 15, i953 UNITED Silt-5S FPFEQE DETONATEQN SUPPREZNTERNAL-CQMBU This invention relates generally to internal combustionengines and to means for suppressing irregular burning and detonation offuel-air mixture therein. The invention is based on my discovery thatdetonation in combustion engines involves acoustic phenomena and can bealleviated by means of certain acoustic apparatus used in combinationwith the combustion chamber.

The present application is directed to improve ments in the fieldcovered by Patent No. 2,573,536, issued October 30, 1951, and entitledEngine Detonation Control by Acoustic Methods and Apparatus. The presentapplication is a continuation-in-part of my application Serial No.252,318, filed October 24, 1951, for Engine Detonation Control byAcoustic Methods and Apparatus, which latter application is a divisionof my parent application which resulted in said Patent No. 2,573,536.For a full discussion of the acoustic aspect of detonation incombustion, and my basic solution for controlling detonation incombustion, reference should be had to my said issued patent.

Only briefly stated herein, the present invention is based on the factthat detonation in an engine combustion chamber produces sound waves, alarge part of which rise to high amplitude at resonant frequencies ofthe chamber, and on my discovery that the sound waves produce many ofthe various well-known and harmful manifestations of detonation.According to my basic invention, I inhibit or attenuate these harmfuleffects by interfering with or attenuating the high amplitude,detonationdnduced sound waves, and this is done by use in conne tionwith the combustion chamber of acoustic tenuation means made responsiveto (operative at) the frequencies or Wave lengths at whichdetonation-induced sound waves build up to high amplitudes. One type ofacoustic attenuation means broadly disclosed in my patent involved anattenuative configuration given to the upper end portion of the piston.

The general object of the present invention is the provision of animproved detonation controlling sound wave attenuator of the classinvolving the piston structure.

A further object is the provision of a novel piston type of detonationattenuator which has good frequency response characteristics to thefrequency range at which offensive detonation is encountered.

A still further object is the provision of a piston type of detonationattenuator of improved structual simplicity.

SSION PISTON FOR STIUN ENGKNES A present illustrative embodiment of theinvention is shown in the accompanying drawing, in which:

Figure 1 is an elevational view of a piston equipped with detonationattenuator characteristics in accordance with the invention, the pistonbeing shown in an engine cylinder; and

Figure 2 is a plan view of the piston shown in Figure l.

The attenuator of the present invention is of a type, first disclosed inmy said issued Patent No. 2,573,536, employing an exponential type horn,which is designed to receive the offensive detonation-inspired soundwaves without reflection back and to conduct such waves to a sound waveattenuative means at its throat Such a horn must be properly designed torespond properly for the wave frequencies to be subdued, and informationon this subject is found in my said issued patent. According to thepresent inven tion, such a horn and attenuative means is provided by aunique configuration or the upper end portion of the piston.

Referring now to the drawings, numeral 8 designates an engine combustionchamber into which opens engine cylinder 9, and numeral Hi designatesgenerally a piston in said cylinder having one ring groove it above thewrist pin, and two ring grooves l i below the wrist pin, these groovesreceiving conventional piston rings, as indicated. The upper end portion12 of the piston, above upward ring groove H, is convergent in an upperdirection, and is configured to provide a horn type space it between itand the cylinder wall it. The upper end portion l2 of the pistonconverges substantially on an exponential function curve i l, in suchmanner that the crosssectional area of the annular space it? between thepiston and the cylinder wall converges downwardly from the top of thepiston in the manner of an exponential type horn. It might here bementioned that while an exponential horn shape is here principallyreferred to, some deviation from a true exponential curve is, inpractice, permissible without loss of the substantial benefits of theinvention. An equivalent but slightly modified shape which isadvantageous in practice is a catenoidal horn. Other equivalent shapesare also feasible, including hyperbolic, and in general, the broadrequirement is that the horn be of the usual flared type used forcoupling pur poses in acoustic practice.

The horn passage 15 is reduced to relatively small transverse dimensiontoward the lower end, and below the point at which the transverse(iimension has been reduced to a millimeter or thereabouts, the passagedevelops sound wave attenuative characteristics for detonation wavefrequencies because of frictional scrubbing of the high velocityoscillating gas particles in the r& stricted passage. It is thus properto say that the lower region of the horn passage, between the piston andthe cylinder wall, functions as a sound wave attenuator, which isfrequency responsive to, i. e., operative at, the detonation wavefrequencies, while the upper portion of the passage functions as acoupling means for conducting the detonation sound waves downwardlyaround the upper end portion of the piston to the attenuator withoutsubstantial reflection back.

In operation, a detonation pressure wave initiated within the combustionchamber of the engine, above the piston, enters into the large upper endof the horn passage l5, and travels down said passage to the narrowthroat portion thereof with ever increasing energy-density, and withoutreflection. This wave encounters and transverses the fine-dimensionlower portion of the where conditions are favorable for dissipation ofthe wave, explained above. Also, the acoustic pressure wave, with itsenergydensity greatly increased in the lower regions of the horn-lilzepassage, acquires a very steep wave front, and a conversion to thissteep wave front is accompanied by creation of high frequency wavecomponents which are conducive to still greater wave attenuation. Theresult is a substantial dissipation of the energy of the wave conducteddown the horn passage, and therefore substantial energy loss by thesound wave in the combustion chamber above. Such energy drain reducesthe tendency of the acoustic wave in the combustion chamber to build upto the substantial amplitudes of detonation.

If a true exponential curve is employed for the horn passage :5, thelower portion of such, which constitutes the wave attenuator, maycontinue its reduction in transverse dimension to the lower end of thepiston portion i2. Alternatively, a catenoidal horn passage may be used,the characteristics of which are that the walls of the passage becomeparallel at the throat. Using such a curve, the convergence may continueuntil a transverse dimension of about a millimeter, or less, is reached,and may then continue downwardly at such dimension.

Thus, the downwardly converging horn passage between the upper endportion 12 of the piston and the cylinder wall picks up the detonationwave from the combustion chamber and directs it downwardly to its lowerend region, where it has definite attenuative or energy-dissipativecharacteristics.

As is well known, a true exponential horn doubles its cross-sectionalarea for equal increments of length. Of course, so far as the generalexponential law goes, the equal increments of length are not fixed atany specific value. What is known as the expansion ratio of the horndepends upon the value at which these equal increments of length aretaken in the design of the horn. The ability of the exponential horn torespond to, or accept without reflection waves of any given frequencyrange, is intimately related to this expansion ratio, and it accordinglybecomes desirable to design an exponential curve with proper accounttaken for the frequency or wave length of the detonation waves which areto be attenuated. Directions for such design are set forth in myaforesaid issued Pat- 4 ent No. 2,573,536, to which reference is heremade.

The piston type attenuator as described is capable of a substantialdegree of attenuation for a detonation-induced sound wave in thecombustion chamber. It is of course necessary in any given case to seethat the physical dimensions of the horn type passage and its attenuatorare proper for the frequency and wave length of the particulardetonation-induced sound wave that is to be subdued. In any givenengine, it is first necessary to determine the frequency of thedetonation wave which is to be subdued. With this information, and withthe directions given here and in my aforementioned Patent No. 2,573,536,those versed in the science of acoustics can readily design thenecessary configuration for a proper frequency responsive horn passageand attenuator.

It will be understood that the drawings and description are illustrativeonly, and that various changes in design, structure and arrangement maybe made without departing from the spirit and scope of the invention asdefined by the appended claims.

I claim:

1. For use with an internal combustion engine having a combustionchamber and cylinder opening into chamber, a piston adapted forreciprocation in said cylinder, the upper end portion of said pistonhaving an outer side sur face spaced from the opposed surface of thecylinder, so as to furnish a downwardly extending sound wave passage,and an acoustic attenuation means for the detonation wave frequencies atthe lower region of said surface.

2. The subject matter of claim 1, wherein said surface of said pistonhas a substantially exponential shaped profile in a plane talacn throughthe longitudinal axis of the piston.

3. The subject matter of claim 1, wherein said surface of said piston aprofile forming, with the opposed surface of the engine cy a downwardlyconverging sound wave whose cross-sectional area tape s in the manner ofa flared acoustic horn.

i. The subject matter of claim 1, wherein a d surface of said piston hasa profile forming, with the opposed surface of the engine cylinder, 21downwardly converging sound wave passage whose cross-sectional areatapers substantially in the manner of an exponential horn.

5. The subject matter of c 1, wherein said surface of said piston has aprofile forming, with the opposed surface of the engine cylinder, 2.downwardly converging sound wave passage whose cross-sectional areatapers in the man-- nor of a flared acoustic horn, the lower region ofsaid piston surface approaching closely to the surface of the enginecylinder, so as to provide said attenuator means in the form of anarrow, downwardly extending sound wave passage region.

6. The subject matter of claim 1, wherein said surface of said pistonhas a profile forming, with the opposed surface of the engine cylinder,a downwardly converging sound wave whose cross-sectional area tapers inthe manner of a flared acoustic horn, the lower end portion of saiddownwardly convergin passage merging with a narrow, downwardly extendingclearance space between the piston and cylinder side wall to form saidacoustic attenuation means.

7. The subject matter of claim 6 wherein said surface of said piston isan uninterrupted surface of revolution about the longitudinal axis ofthe piston.

8. The subject matter of claim 1, wherein said surface of said pistonhas a profile forming, with the opposed surface of the engine cylinder,an annular, downwardly converging sound wave passage whosecross-sectional area tapers substantially in the manner of anexponential horn, the lower region of said piston surface approachingclosely to the surface of the engine cylinder, so as to provide saidattenuation. means in the form of a narrow, downwardly extending soundwave passage region.

9. For use with an internal combustion engine having a combustionchamber and a cylinder opening into said chamber, a piston adapted forreciprocation in said cylinder, the upper end portion of said pistonhaving an outer side surface spaced from the opposed surface of thecylinder, said surface of said piston having a shaped profile to formbetween it and. the opposed surface of the cylinder a downwardlyextending sound Wave passage whose cross sectional area convergesdownwardly in the manner of a flared acoustic horn, the lower portion ofsaid outer side surface of said piston closely approaching the opposedsurface of the cylinder so as to provide an attenuator for detonationwave frequencies.

ALBERT G. BODINE, JR.

References Cited in the file of this patent FOREIGN PATENTS Number

